[04/17] Fix deep C-state TSC desynchronization

Commit Message

Zachary Amsden June 15, 2010, 7:34 a.m. UTC

None

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c8289d0..618c435 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1822,7 +1822,18 @@  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	kvm_x86_ops->vcpu_put(vcpu);
 	kvm_put_guest_fpu(vcpu);
+
 	vcpu->arch.last_host_tsc = native_read_tsc();
+
+	/*
+	 * When potentially leaving a CPU with unstable TSCs, we risk
+	 * that the CPU enters deep C-state.  If it does, the TSC may
+	 * go out of sync but we will not recalibrate because the test
+	 * vcpu->cpu != cpu can not detect this condition.  So set
+	 * vcpu->cpu = -1 to force the recalibration above.
+	 */
+	if (check_tsc_unstable())
+		vcpu->cpu = -1;
 }
 
 static int is_efer_nx(void)